If the discussion is moving to the size range of something that can wrap around a 32 oz Nalgene bottle, there are numerous possibilities:

1) a stainless steel cup specifically sized to fit a Nalgene. Commonly available, it takes up little space, will heat a significant amount of water, and is quite durable. Drawback is that it is fairly heavy.

2) a Snow Peak 700 cup - titanium, which means it is pricy, but it is very light and extremely tough. I swallowed hard and bought one of these last year. It was worth it. Larger capacity - it is really all you need for a minimal cook kit, and it comes with a lid.

I would love to see an aluminum version of these cups. It would be light, cheap, and not quite so durable, but I have not found one.

A metal cup that will fit a shirt pocket PSK is a real toughy, as this thread demonstrates. The closest is the old Tacoma Mountain Rescue PSK which is contained in a tobacco can (Prince Albert). Just a little too big to really fit in the average shirt pocket, but it can produce a reasonable amount of liquid from snow.

I would hate to melt snow in an Altoids tin, but if that was all you had.......